1. Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer into a plurality of individual devices along a plurality of crossing streets formed on the front side of the wafer, the wafer being composed of a substrate and a functional layer formed on the front side of the substrate, the functional layer being composed of an insulating film and a functional film formed on the insulating film, the individual devices being formed from the functional layer and partitioned by the streets.
2. Description of the Related Art
As well known in the art, in a semiconductor device fabrication process, a functional layer composed of an insulating film and a functional film is formed on the front side of a substrate such as a silicon substrate, and a plurality of devices such as ICs and LSIs are formed like a matrix from this functional layer, thus obtaining a semiconductor wafer having the plural devices. The plural devices are partitioned by a plurality of division lines called streets formed on the front side of the semiconductor wafer. The semiconductor wafer is divided along these streets to obtain the individual devices. Division of the semiconductor wafer along the streets is usually performed by using a cutting apparatus called a dicing saw. This cutting apparatus includes a chuck table for holding the semiconductor wafer as a workpiece, cutting means having a cutting blade for cutting the semiconductor wafer held on the chuck table, and moving means for relatively moving the chuck table and the cutting means.
In recent years, a semiconductor wafer intended to improve the processing performance of devices such as ICs and LSIs has been put into practical use. This semiconductor wafer is composed of a substrate such as a silicon substrate and a functional layer formed on the front side of the substrate. The functional layer is composed of a low-permittivity insulator film (Low-k film) and a functional film formed on the Low-k film, the functional film forming a plurality of circuits. Thus, the devices are formed from the functional layer. For example, the Low-k film is formed of a glassy material such as SiO2, SiO, and SiN. The Low-k film is different in material from the substrate constituting the wafer, so that it is difficult to cut the substrate together with the Low-k film by using the cutting blade. That is, the Low-k film is very brittle like mica. Accordingly, when the semiconductor wafer having the Low-k film is cut along the streets by using the cutting blade, there arises a problem such that the Low-k film may be separated and this separation may reach the circuits to cause fatal damage to the devices.
To solve this problem, Japanese Patent Laid-open No. 2009-21476 discloses a wafer dividing method including the steps of forming a laser processed groove along each street formed on the semiconductor wafer to thereby remove the functional layer along each street and next cutting the semiconductor wafer along each street by using a cutting blade in such a manner that the cutting blade is aligned with each laser processed groove where the functional layer is absent and the cutting blade and the semiconductor wafer are relatively moved.